Radius and performance

Hello, all. It's a question to all members of freeradius community :) I'm going to use freeradius in my billing system. That's why i'd like to know, what is the maximum loading on the freeradius-server (average number of online users during the day, total number of users, interval of alive packets etc.). Maybe there is some tests of freeradius's perfornance or maybe someone is using freeradius in his billing system... It would be very interesting for all members of community. Thanks beforehand.